In optics fields, optical shutter plays an important role for getting high quality image, and controlling the light. For having shutter function for the optical devices, many methods and apparatuses are invented and currently used.
Mechanical shutter is most widely used for the optical systems. Light reflecting plate or light absorbing plate is used for blocking the input light and is controlled by the mechanical structure. One of the examples of mechanical shutter can be found in U.S. Pat. No. 6,762,866. Fast moving metal blade blocks the laser light or unblocks the laser light. The blade is controlled by the solenoids or AC or DC motors that can be rapidly operated by the shaped electrical pulses. Diaphragm structure is also introduced for having better quality and speed.
Liquid crystal can also be used for building the optical shutter which is described in U.S. Pat. No. 5,455,083. Nematic liquid crystal is applied for the optical shutter function. The liquid crystal cluster can be aligned for blocking the light and also can be aligned for transmitting the light. To enhance the performance of the optical shutter function, additional polarizing optics can be applied to the system. Liquid crystal optical shutter has low contrast ratio and slow shutter speed.
For fast controlling of the light especially laser light, satiable absorber can be applied to the optical shutter system. The schematics of the optical shutter using satiable absorber are described in the U.S. Pat. No. 6,757,094. A photon absorbing layer is applied to the system and when light is passing the layer, the light is absorbed up to a certain level. Beyond this level, the material becomes transparent and the layer does not block the light any more. The saturation process is very fast and the optical shutting time also can be very fast. Since the process is only controlled by the absorbing process of the light, extra light control system is required for the system and the speed is only determined by the satiable absorbing material properties. For fast shuttering the optical signal, a Pockel's cell is also used. Electro-optics effect is used and the polarization change makes the optical shutter work.
Optical shutter function using interference effect is another method for optical shutter, which is described in the U.S. Pat. No. 6,965,477. A movable filter is applied to the system to control the light transmission or reflection. The gap between the fixed layer and the movable layer is determined by the incident light wavelength to make constructive or destructive interference of the incident light. Since the structure should be controlled within wavelength of the incident light, the optical shutter is difficult to control and gives undesired error due to the motion control error.
For a small beam size, micro electro mechanical system (MEMS) is applied to get a optical shutter function. A block translated by the micro-electric actuator to block the incident beam or unblock the beam even to control the amounts of the incident beam. Those kinds of micro-mechanical shutter systems are described in the U.S. Pat. No. 6,901,204 and U.S. Pat. No. 6,972,899. Since the MEMS device is small and fast for the optical shutter, MEMS device can be used as a good fast working optical shutter only if it can be made for optical shutter.